The present invention relates to semiconductor laser devices and methods of manufacturing the same. More particularly to such devices which have high-power low-noise characteristics effective for use as optical sources for erasable optical discs and methods of manufacturing such devices.
Self-sustained pulsating semiconductor laser devices are used as low-noise semiconductor laser devices. However, in conventional self-sustained pulsating semiconductor laser devices, the kink power and the maximum optical output which enables the self-sustained pulsation is low, for example, about 7-9 mW, as disclosed in Japanese papers, IECE TECHNICAL REPORT ON OPTICAL AND QUANTUM ELECTRONICS,OQE 84-57 (1984), pp. 39-46 and OQE 84-30, pp. 65-72.
Self-sustained pulsating semiconductor laser devices having an active layer of a double heterostructure and an active layer of a multiquantum well structure and the characteristics thereof are disclosed, for example, in the Inventors' article entitled "Self-sustained Pulsating Semiconductor Lasers with a Ridge Stripe Structure", Japanese paper, IECE TECHNICAL REPORT ON OPTICAL AND QUANTUM ELECTRONICS, OQE 88-5 (1988), pp. 33-38. The technique disclosed in this report is incorporated in the present invention.
Conventionally, the single quantum well structure of the semiconductor lasers is mainly used for reducing their threshold current. In addition, a pair of superlattice waveguides are provided one on an upper surface of the single quantum well active layer and the other on a lower surface of the layer in order to improve the flatness and crystallinity of the quantum well interface. Semiconductor laser devices of this type are disclosed, for example, in Japanese paper, EXTENDED ABSTRACTS (THE 46TH AUTUMN MEETING, 1985), THE JAPAN SOCIETY OF APPLIED PHYSICS, 1P-N-8, P. 196.
Self-sustained pulsating semiconductor lasers are conventionally suitable for low-noise semiconductor lasers required as optical sources for light video discs, etc. The characteristics of the self-sustained pulsating semiconductor lasers are addressed, for example, in Japanese paper, IECE TECHNICAL REPORT ON OPTICAL AND QUANTUM ELECTRONICS, OEQ 84-30, pp. 65-72. As described above these semiconductor lasers, the kink power and the optical output power which enables self-sustained pulsation are low, and 7-9 mW. In addition the control of the self-pulsating frequency is not studied and the frequency is high, for example, about 1 GHz.
Conventionally, an optical waveguide is etched with an etchant to form a ridge stripe structure, and the control of the thickness of the waveguide has been provided by setting an etching time in consideration of the etching rate of an etchant. References concerned are, for example, Japanese papers, EXTENDED ABSTRACTS (THE 35TH SPRING MEETING, 1988), JAPAN SOCIETY OF APPLIED PHYSICS AND RELATED SOCIETIES, 31p-ZP-17 (1988), p. 912 and IECE TECHNICAL REPORT ON OPTICAL AND QUANTUM ELECTRONICS, OQE 88-5 (1988), pp. 33-38.